Crossed field electron tube having input and output cavities and drift region defined by a pair of high conductivity non-magnetic plates



A ril 23, 1968 C M. GARRETSON CROSSED FIELD BLECTROWTUBE HAVING INPUT AND OUTPUT CAVITIES AND DRIFT REGION DEFINED BY A PAIR OF HIGH Filed April 6, 1964 CONDUCTIVITY NON-MAGNETIC PLATES 2 Sheets-Sheet 1 Jamal, 0M

Apnl 23, 1968 c. M. GARRETSON 3,379,921

CROSSED FIELD ELECTRON TUBE HAVING INPUT AND OUTPUT CAVITIES AND DRIFT REGION DEFINED BY A PAIR OF HIGH CONDUCTIVITY NON-MAGNETIC PLATES Filed April 6, 1964 2 Sheets-Sheet 2 FIG. 5

F/ELD H HHHI H\ 32 WA V55 6 5' 37 57 INVENTOR.

United States Patent M ABSTRACT OF THE DISCLOSURE This invention relates to the art of electron tubes, more particularly of the type capable of generating relatively great power in the ultra high frequency range. The electron tube imparts energy to an electron beam in a launch region and then causes the electron beam to move to an interaction region where the electron beam by the application of a small amount of RF energy converts the DC energy to a substantial amount of RF energy.

As conducive to an understanding of the invention, it is noted that where an electron tube is employed to amplify or act as an oscillator in the ultra high frequency range corresponding say to wavelengths in the millimeter region and such tube requires that the physical distance between elements in the tube be a fraction of a wavelength in order that there will be the shortest possible time of passage of the electrons in the tube in order not to reduce the RF field encountered by the electrons, as the length of the interaction region becomes increasingly small with increase in frequency, the amount of power that can be handled without overheating is severely limited and in fact it is difiicult to manufacture such a tube for ultra high frequency due to physical limitations in the size of the elements.

Where, to solve this problem, electron tubes such as a helical beam tube are used in which the electrons are caused to rotate in synchronism with an RF field by means of a magnetostatic field and the electrons are grouped into a bunch in one interaction region and their energy is extracted from such region by a suitable wave guide, since the optimum phase relation for grouping and for energy extraction cannot be achieved simultaneously in one interaction region, such device is extremely inefiicient.

It is accordingly among the objects of the invention to provide an electron tube whose interaction structure may be extended in size in all dimensions, thereby permitting operation at frequencies and powers greatly in excess of those possible with the prior art.

It is a further object to provide an electron tube whose interaction system is inherently of high efficiency.

It is still a further object to provide an electron tube whose interaction system is such that its mechanical design can be of great simplicity, thereby greatly facilitating its manufacture for operation at very high frequencies and powers.

According to the invention, an electron beam is caused to move from an electron emitting surface, through a multiplicity of electromagnetic circuits separated by drift structures, and finally to a collecting means in which the electron beam is captured. This movement is achieved by using electrostatic and magnetostatic fields at right angles to each other, and also at right angles to the linear movement of the beam. The movement of the beam is com- 3,379,921 Patented Apr. 23, 1968 posed of a linear part which causes the electrons to progress through the several regions of the tube, and a rotary part which causes the electrons to circle about the magnetostatic field lines, and which causes the interaction with the RF fields to take place. The magnitude of the magnetostatic field is adjusted to a value which causes the rotary motion of the electron to complete one cycle in the same time as the RF field completes one cycle so that cumulative interaction over an extended region will occur.

The electromagnetic circuits, which typically might be RF shorted wave guides which are iris coupled to the input and output circuits, are designed to support standing waves of RF fields, so that in progressing in a direction transverse to the linear beam movement, a peak of one phase of RF field is followed by a node, which is followed by a peak of phase opposite to the first encountered, which in turn followed by a node, and then a peak of the same phase as the first encountered, and so on. The peaks of RF magnetic field occur at the nodes of RF electric field, and vice versa.

In the bunching circuit, the electrons are acted upon by forces which arise from the rotary motion of the electrons and the RF magnetic field in accordance with well known principles of electromagnetic theory. Those electrons which reach the positive peak of their rotary motion when the RF magnetic field is directed in a positive direction will be cumulatively directed toward an RF magnetic field node in one direction, while those electrons which reach the positive peak of their rotary motion when the RF magnetic field is directed in a negative direction will be cumulatively directed toward an RF magnetic field node in the opposite direction, in both cases the grouping motion being parallel with the magnetostatic field. Non-peak electrons will exhibit the same tendency to bunch, although the forces will be less for the nonpeak cases. It is by the means of RF magnetic standing waves that this invention achieves the separation of the electrons into phase groups, one phase group tending to occur at one RF magnetic field node, and another phase group tending to occur at an adjacent RF magnetic field node, and so on successively along the standing wave pattern in the electromagnetic circuit. This tendency to group is brought to completion in a drift structure, in a fashion analogous to the action in a conventional klystron.

It is an essential aspect of this invention that the phase grouping above described is achieved in a region separate and distinct from the region in which energy 1s extracted from the electron beam. The energy extraction is achieved in an electromagnetic circuit positioned after the drift structure. The RF magnetic field nodes in this energy extraction electromagnetic circuit are in register with the RF magnetic field nodes in the bunching electromagnetic circuit, or, from the nature of standing waves, the RF magnetic field nodes about which the electrons are phase grouped, are centered on the RF electric field peaks in the energy extraction electromagnetic circuit. The separation of bunching and energy extraction region makes it possible to achieve the proper phasing of the electrons for optimum interaction in both cases; in the bunching region the peak of the electron rotary motion is in phase with the peak RF magnetic field; in the energy extraction region, the peak of the electron rotary motion is in phase with the peak RF electric field. (RF electric fields and RF magnetic fields being in time quadrature for standing waves. Besides the optimizing of the energy extraction phase in the energy extraction region, the use of standing waves also aids in preventing debunching during energy extraction by virtue of the fact that the electrons tend to be grouped in the region of minimum RF magnetic field, that is, Where debunching forces are minimized.

In summary, according to this invention, extended interaction, permitting large interaction structures, is achieved by synchronizing the rotary motion of the electron with the RF field to be amplified. To assure only desirable interactions, the grouping of the electrons by standing RF magnetic fields into phase groups centered on RF magnetic field nodes is initiated in a region separate from the energy extraction region in which standing RF electric fields extract the energy. The two regions are separated by a drift structure which is vital in letting the grouping initiated in the bunching region go to completion.

In the accompanying drawings in which is shown ne of various possible embodiments of the several features of the invention.

FIG. 1 is a side elevational view of one embodiment of the invention,

FIG. 2 is a sectional view taken along line 22 of FIG. 1,

FIG. 3 is a fragmentary sectional view of the interaction region taken along line 33 of FIG. 2,

FIG. 4 is a sectional view taken along line 4-4 of FIG. 3 showing the heater and input and Output cavities,

FIG. 5 is an enlarged view of a portion of FIG. 3 diagrammatically illustrating the paths of some representative electrons, and

FIG. 6 is a detail view on an enlarged scale of the cathode.

Referring now to the drawings, the embodiment shown comprises an inter-action chamber 11, which is maintained under a vacuum and which illustratively has an external electro'magnet M illustrative of the C type associated therewith, although it is understood that other types of magnets can be used.

The chamber 11 comprises an annulus 12 which forms the side wall thereof with a top and bottom closure plate 13, 14 respectively, all being of non-magnetic material such as stainless steel so that the magnetic field of the magnet M will not be weakened or disturbed.

The chamber 11 has a port 14' in side wall 12 in which is secured a sleeve 15 over the mouth of which is secured a plate 16 which defines an input-output window and is made from a material transparent to RF energy such as ceramic or glass, for example.

Positioned in the chamber 11 is an electrostatic shield 17 which has an extension 18 passing into the sleeve 15.

The shield has two parallel rectangular wave guides 21, 22 therein, the ends of which are flared outwardly as at 21, 22' to define electromagnetic horns.

The horns 21', 22 at the outer end of extension 18 are in juxtaposition to and spaced from plate 16 and define the output and input respectively of the unit.

Positioned in the chamber 11 are parallel juxtaposed spaced plates 24, 25, made of non-magnetic, low electrical loss material such as copper, and which have juxtaposed rectangular grooves 26 in the opposed surfaces 24', 25' thereof defining a wave guide with flared ends which define a horn 27 aligned with the horn 22' of the wave guide 22. The electrostatic shield restricts the electrostatic field between plates 24, 25 from wandering to regions where it could cause electrostatic breakdown and at the same time provides means for guiding the input and output power.

The inner end of the wave guide defined by grooves 26 leads into an input cavity 28 defined by juxtaposed grooves 28' in the opposed surfaces of plates 24, 25. The input cavity 28 thus is a resonator slit along its center line to provide insulation between ,plates 24, 25 and to provide for passage of the electron beam.

The cavity 28 has an inductive input iris 29 which determines the standing wave ratio in such input cavity and regulates the flow of power to such input cavity 28.

The plates 24, 25 have juxtaposed grooves 32' in their opposed faces which define the output cavity 32 that is longitudinally spaced from input cavity 28 and similar thereto, the space between such cavities defining the drift space.

The output cavity 32 has an inductive output iris 33 which determines the standing wave ratio of such cavity and regulates the amount of power to be transmitted to the load. Iris 33 is in communication with wave guide 34 formed by opposed rectangular grooves in the opposed faces of plates 24, 25, the outer end of wave guide 34 being flared to define a horn 35 aligned with horn 21' of wave guide 21 so that energy may be fed to the outlet horn 21 to be radiated through the window 16.

As shown in FIGS. 3 and 4, the plate 24 has a recess or slot 40 between the input cavity 28 and the adjacent end 40' of the plate.

The inner face of plate 24 has a protruding portion 36 through which the slot 40 extends and the rear of the protruding portion is sloped as at 36' to define a ramp whose function is to provide optimum spacing between plates 24, 25 at the region where the electron beam is launched from the cathode 41.

As shown in FIGS. 4 and 6, the cathode 41 which is positioned in the slot 40 contains a heater 37 for which the electric return 37 is attached to plate 24. A mount lock 38 in the rear of slot 40 secures the heat shield 38' which supports the cathode 41, the latter emitting electrons when heated which flow toward cavity 28.

As shown in FIG. 2, the plate 25 is retained in fixed position in chamber 11 by means of insulated supports 43 extending radially inward from the wall 12 of the chamber 11. Plate 24 is retained in fixed position in chamber 11 by means of supports 42 which illustratively are conductors extending radially inward from the wall 12 of the chamber 11.

Positioned in chamber 11 is a collector 51 mounted by insulated supports 52 to the wall 12 of the chamber. The wall 12 has an opening 53 illustratively diametrically aligned with opening 14' and a sleeve 54 is secured in said opening. A lead 55 secured at one end to the collector 51 extends axially through sleeve 54 and through an insulator 50, the end of which has a terminal (not shown) to permit connection of a source of positive potential to the collector 51.

As shown in FIG. 2, the end 48 of the collector and the adjacent end 48' of plate 25 are beveled to define a tapered passageway 49, the spacing of which determines the position of capture of the electrons flowing to the collector and permits collection of each electron at its minimium energy thereby increasing the efiiciency of the unit.

To energize the heater 37, a lead 57 is connected thereto which is connected to a lead 58 that extends axially through a sleeve 61 secured at one end in an opening 59 in wall 12 and through an insulator 60 at the end of the sleeve which has a heater voltage terminal 60.

The wall 12 also has an opening 62 diametrically 0pposed to opening 59 and in which one end of a sleeve 63 is secured. Extending axially through the sleeve 63 and through a high voltage insulator 71 at the end thereof is a high voltage lead 64 connected to a high voltage terminal 65 at the end of insulator 71. The inner end of lead 64 is connected to plate 25 as shown in FIG. 2 so that a high positive voltage may be applied thereto to provide a high electrostatic field between the plates 24, 25.

It is this high electrostatic field combined with the magnetic field developed by the magnet M that causes the electrons emitted by cathode 41 to move along a trochoidal path from the cathode to the collector.

The chamber 11 and the sleeves 15, 54, 61 and 63 connected thereto are all vacuum sealed and by reason of the elongated sleeves, the seals which may be located at the point of connection of the insulators 50, 60, 71 and plate 16 to the sleeves may be in a region of low or zero magnetic fields, thereby permitting a wide choice of sealing materials and in particular permitting magnetic materials to be used.

In order to maintain a high vacuum in the interior of the unit, an ion pump 73 of conventional type is associated with sleeve 63 as shown in FIG. 1.

Operation In the operation of the unit, RF energy is radiated through window 16 by means of an electromagnetic horn and received by a corresponding horn 22' in electrostatic shield 17. It is then transmitted through the shield 17 by means of rectangular wave guide 22; radiated by associated horn 22 into horn 27 and transmitted into cavity 28 through rectangular wave guide 26, the gap between plates 24, 25 not being deleterious to RF power propagation in the dominant TE mode.

When the cathode 41 is heated, electrons emitted from the cathode will move toward the input cavity 28 and thence through the drift space determined by the gap between plates 24, 25 to the output cavity 32 and finally to the collector 51, following a trochoidal path under the action of the electrostatic field caused by the high voltage applied to plate 25 and the magnetostatic field supplied by magnet M.

Once the applied voltages and magnetostatic field are fixed, the relative time spent in each region of the interaction part of the tube depends only on the relative spacing of the interaction plates 24 and 25; and in the collector region, on the relative spacing of the interaction plate 25 and the collector 51. The ramp 36' and the contour of the collector 51 are thus means of controlling transit time in the region by adjusting spacing. The spacing also affects the character of the trochoidal path, and permits the electron beam to be cycloidal at emission, to be almost entirely rotary at the input and output cavities 28 and 32, and then to be cycloidal at the collector (this latter being only partially realizable since the beam is no longer homogeneous at this point due to electrons yielding various amounts of their energy to the output cavity 32). It is this ability to adjust the beam for cycloidal collection which permits high efficiency to be obtained.

The electronic interaction may be understood from FIG. 4. The electrons are emitted from the cathode 41 and under the action of the electrostatic and magnetostatic fields move to the input cavity 28. Here they encounter RF magnetic and electric standing waves positioned as indicated at the left of FIG. 5. The RF magnetic field acts upon the rotating electrons causing them to move transverse (up and down on FIG. 5) to their general motion. According to their rotary phase, relative to the RF phase, the electrons will move up or down an amount proportional to the magnitude of the RF magnetic field at the point considered. Thus, in FIG. 5 those electrons of a rotary :phase represented by the solid lines will move upward in the upper portion of FIG. 5, and downward in the lower portion because the RF magnetic field reverses its phase at the centerline of FIG. 5. The broken lines representing electrons with a rotary phase opposite to the foregoing, will move in the opposite direction.

Once given a velocity in a certain direction in the input cavity 28, the electrons will continue to move in that direction in the drift structure between the input cavity 28 and the output cavity 32. The total amount of transverse displacement will -be proportional to the distance travelled in the general direction of electron movement.

The net effect of this transverse movement up or down according to phase is a grouping of electrons of similar phase about points in the output cavity 32 which will sustain peak RF electric fields, provided the input cavity fields and output cavity fields are in the register. The impingement of the electron groups causes an RF electric field to be created. Once the RF field in the output cavity 32 reaches a steady value whose magnitude is governed in part by the output cavity iris 33, the power to the output cavity 32 from the electrons is transmitted through the output wave guide 34 to the external load at a steady value.

It is essential that different phase relationships exist in the input cavity 28 and the output cavity 32. Thus, in the input cavit 28, the electrons reach their peak at the same time as the RF magnetic field. In the output cavity 32, the electrons reach their peak at the same time as the RF electric field. It is this difference in relative phase which permits a minimum energy interchange in the input cavity 28 and a maximum energy interchange in the output cavity 32.

Thus, the separation of input and output cavities serves not only to permit the bunching to go to an optimum completion, but allows the all important phase relationship to be established.

Thus, with the unit above described in which separate input and output cavities are provided, maximum power output at high frequencies can be obtained.

As many changes could be made in the above system and equipment, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. An electron tube comprising a vacuum envelope, a pair of plates in said envelope of high conductivity non-magnetic material insulated from each other, each of said plates having a pair of longitudinally spaced rectangular grooves in the opposed faces thereof forming cavities which define input and output RF standing wave means respectively, and inductive input iris at one end of each of said cavities, each of said opposed faces of said plates having two pairs of aligned parallel rectangular grooves extending longitudinally thereof, each of said pair of aligned grooves defining a waveguide connected at one end to the associated iris and being tapered outwardly at its other end to define an RF horn for coupling to an external source of RF power and to an external load respectively, the space between aforesaid cavities defining a drift region, means for providing a difference of potential between said plates, a collector in said envelope to receive electrons after they have passed said output RF standing wave means, means to emit electrons for flow through said input standing wave means, said drift region and said output standing wave means to said collector and means to provide a magnetostatic field parallel to the RF standing waves in the input and output standing wave means and perpendicular to the electrostatic field caused by the difference of potential between said members and of magnitude so as to cause the rotary motion of the electrons induced by said electrostatic and magnetostatic fields to be in synchronism With the RF standing waves in the input and output standing wave means.

2. The electron tube set forth in claim 1 in which said tube has an input and output window, an electrostatic shield is interposed between said window and the electrostatic field of said spaced plates and wave guides are provided through said shield for transmittal of the external source of RF power to the input cavity and for transmittal of power to the external load.

3. The combination set forth in claim 1 in which one of the spaced plates has an inwardly extending portion in the space between the plates positioned between the input cavity and the adjacent end of the plate and a slot extends through said inwardly extending portion, a cathode is positioned in said slot and heater means are provided to energize said cathode.

4. The combination set forth in claim 1 in which one 7 of the spaced plates has an inwardly extending portion in the space between the plates positioned between the input cavity and the adjacent end of the plate and a slot extends through said inwardly extending portion, a cathode is positioned in said slot, heater means are provided to 5 energize said cathode and the difference in potential is provided by applying a potential to the other of said plates that is positive with respect to the slotted plate accommodating the cathode.

References Cited UNITED STATES PATENTS 3,085,207 4/1963 Ashkin 3304.7 3,175,163 3/1965 Johnson 330-4] HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner.

P. L. GENSLER, Assistant Examiner. 

